JPH069964B2 - Electric brake booster - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a brake booster, and more particularly to a small size of the device itself by using an electric motor and a ball screw that converts its rotational force into an axial force. The present invention relates to an electric brake booster device that can contribute to realization.

[Prior Art] As a conventional vehicle brake booster, a vacuum booster and a hydraulic booster are known. The vacuum booster uses negative air pressure as its pressure source, so the device itself becomes large to obtain a large pressure, and the hydraulic booster has a large pressure source. It is possible to reduce the size by using the hydraulic pressure that can obtain the pressure, but in any case, these boosters have a fixed boost ratio.

Therefore, efforts have been made to develop a variable booster capable of arbitrarily changing the boost ratio, and a hydraulic variable booster is known as an example. This hydraulic variable booster employs a system in which the booster ratio is variable by putting the hydraulic pressure adjusted by a hydraulic control valve into the booster to control the relationship between pedaling force and deceleration, for example. The use of hydraulic pressure for the control has a structure in which a larger power can be obtained as compared with the use of vacuum or air pressure, and therefore the actuator can be downsized.

[Problems to be Solved by the Invention] However, in the above-mentioned hydraulic variable booster,
A hydraulic control valve for controlling the actuator, a pump and a drive motor as a hydraulic source are required, and even if the actuator can be downsized, the hydraulic source and the hydraulic control valve are large, and the size of the entire device is sufficiently small. Cannot be achieved.
Furthermore, these mechanical devices have a complicated structure and are expensive.

The present invention was devised in order to effectively solve these problems in view of the above problems. Therefore its purpose is
An object is to provide an electric brake booster having a simple structure and a variable boost ratio that can contribute to downsizing of the device itself.

[Means for Solving the Problems] An electric brake booster according to the present invention is located at an inner peripheral portion of an electric motor, and a bearing restrains a position in a rotational axis direction with respect to a housing of the electric motor. The rotor is rotatably supported, and the ball screw has a nut portion and a bolt portion, and the nut portion is fitted and fixed to the inner circumference of the rotor. One end of the bolt portion is in contact with the piston of the hydraulic pressure generator, and the other end is connected to the brake pedal.

[Operation] The electric brake booster of the present invention transfers the rotational force of the rotor of the electric motor via the ball screw that can smoothly convert the rotational movement of the nut portion into the axial reciprocating movement of the bolt portion. The pedaling force transmitted from the brake pedal to the piston is converted into an axial force that doubles.

That is, it is detected that the pedaling force of the brake pedal acts on the bolt portion of the ball screw, the rotor of the electric motor whose axial position is constrained by the bearing rotates, and accordingly, the rotor is fitted and fixed to the inner circumference of the rotor. The nut part of the ball screw also rotates without moving in the direction of the rotation axis. The torque of this nut is converted to the axial force of the bolt,
It acts as an axial force on the piston connected to the other end of the bolt portion.

[Embodiment of the Invention] A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a side sectional view showing an embodiment of the electric brake booster of the present invention, and FIG. 2 is a semi-longitudinal sectional view taken along the line II-II in FIG.

As shown in the figure, an electric motor 1 is used in the brake booster of this embodiment. Reference numeral 2 denotes a stator, and a rotor 3 is provided on an inner peripheral portion of the stator 3 so as to be axially constrained by a bearing 14 and rotatably supported. A ball screw case 4, which rotates integrally with the rotor 3, that is, a nut portion of a ball screw is fitted to an inner peripheral portion of the rotor 3. A piston 5 is screwed into the inner peripheral portion of the ball screw case 4 as a bolt portion of the ball screw. Therefore, the rotational movement of the electric motor 1 is converted into a reciprocating movement of the piston 5 in the axial direction by the ball screw.

A spline shaft 6 is fitted to one end of the piston 5 so as to operate integrally therewith, and the spline shaft 6 is fitted to a ball spline case 8 fixed to a motor housing 7. This prevents the piston 5 from rotating together with the spline shaft 6, and allows only reciprocating movement in the axial direction. The tip of the spline shaft 6 is in contact with a piston 9 of a hydraulic pressure generator (not shown).

On the other hand, an input rod 11 connected to the brake pedal 10 is fitted to the other end of the piston 5, which is the bolt portion of the ball screw.

When the driver depresses the brake pedal 10 to operate the brake, the pedaling force is transmitted to the input rod 11 and presses the piston 5 in the axial direction. At this time, the pedal force sensor 13 provided on the brake pedal 10
Thus, the pedal force is detected, an appropriate current is applied to the motor 1 in accordance with the pedal force, and the motor 1 produces a desired torque and rotates, thereby rotating the ball screw case 4. This rotational force is converted into a force in the axial direction of the piston 5 via the ball screw, and an appropriate boosting action is exerted on the pedaling force transmitted from the brake pedal 10 to the piston 5.

It should be noted that the performance of pulse motors has been remarkably improved in recent years, and small and highly accurate ones have become popular. When this pulse motor is used as the drive source of the booster, when the power fails, the piston 5 is pushed only by the pedal force of the driver, and in order to pull back the piston 5, the elastic force of the return spring 12 provided in the brake pedal 10 is used. The operation is performed only by. Therefore, it is desirable that the rotational torque of the rotor 3 that rotates simultaneously with the movement of the piston 5 is as small as possible. For that purpose, it is preferable to use, for example, a VR type pulse motor.

[Effects of the Invention] As is apparent from the above description, the present invention has the following excellent effects.

That is, since the electric motor is used as the drive source of the booster and the ball screw is used as the drive force transmission device, the device itself can be miniaturized.

In addition, the rotor of the electric motor is rotatably supported by a bearing in the inner peripheral portion of the electric motor, the position of which is restricted in the rotational axis direction, and only the bolt portion of the ball screw moves in the axial direction by the rotation of the rotor. Because it is a structure,
The rotor of the electric motor, which has the largest diameter in terms of structure, only rotates at the same position on the rotating shaft, and a wasteful space larger than the volume of the rotor in the rotating shaft direction is not required inside the electric motor. Therefore, the volume of the entire device can be further reduced.

[Brief description of drawings]

FIG. 1 is a side sectional view showing a schematic configuration of an electric brake booster according to the present invention, and FIG. 2 is a semi-longitudinal sectional view taken along the line II-II in FIG. In the figure, 1 is an electric motor, 3 is a rotor, 4 is a ball screw case as a nut part of a ball screw, 5 is a piston as a bolt part of a ball screw, 9 is a piston of a hydraulic pressure generator, and 10 is a brake pedal.

Claims (1)

[Claims] 1. A rotor, which is located on an inner peripheral portion of an electric motor and is rotatably supported by a bearing so that its position in the rotational axis direction is restrained with respect to a housing of the electric motor, and a nut portion and a bolt portion. A ball screw in which the nut portion is fitted and fixed to the inner circumference of the rotor, one end of a bolt portion of the ball screw is in contact with a piston of a hydraulic pressure generating device, and the other end is connected to a brake pedal. An electric brake booster characterized by.